A branch of economics that concentrates on explaining the economic decisions people make in practice, especially when these conflict with what conventional economic theory predicts they will do. Behaviourists try to augment or replace traditional ideas of economic rationality (homo economicus) with decision-making models borrowed from psychology. According to psychologists, people are disproportionately influenced by a fear of feeling regret and will often forgo benefits even to avoid only a small risk of feeling they have failed. They are also prone to cognitive dissonance, often holding on to a belief plainly at odds with new evidence, usually because the belief has been held and cherished for a long time. Then there is anchoring: people are often overly influenced by outside suggestion. People apparently also suffer from status quo bias: they are willing to take bigger gambles to maintain the status quo than they would be to acquire it in the first place.
Traditional utility theory assumes that people make individual decisions in the context of the big picture. But psychologists have found that they generally compartmentalise, often on superficial grounds. They then make choices about things in one particular mental compartment without taking account of the implications for things in other compartments.
There is lots of evidence that people are persistently and irrationally overconfident. They are also vulnerable to hindsight bias: once something happens they overestimate the extent to which they could have predicted it. Many of these traits are captured in prospect theory, which is at the heart of much of behavioural economics."